1. Field of the Invention
The present invention relates to a mask for used in the fabrication of a semiconductor device, and in particular to an improved optical proximity correction mask (OPCM) for use in fabricating a semiconductor device of which a pattern is corrected in order that a pattern, which is actually printed on a semiconductor substrate, may be fabricated approximate to a desired pattern.
2. Description of the Conventional Art
In a lithography process which employs a light source such as g-line, i-line, or deep ultra violet (DUV), etc., various methods are being studied to overcome a resolution limit. As a part of the studies therefor, in a mask fabrication technique, an optical proximity correction mask (OPCM) is regarded as one of the most effective techniques compared with a phase shift mask (PSM). Particularly, compared with the PSM, the OPCM has a property of a binary mask which is provided only with a light blocking layer and a light projection layer, and thus using the OPCM is more advantageous in terms of manufacturing cost, effectiveness, etc.
In a case where the lithography process using a conventional general mask is performed, the size and shape of a photoresist pattern which is printed onto a semiconductor substrate may be different from that of a pattern of the mask due to an optical proximity effect (OPE). That is, because a lens employed in exposing the pattern of the mask to the light is curved, a corner rounding error of the photoresist pattern printed onto the semiconductor substrate may be occurred, and more excessive corner rounding error leads to a problem such as line shortening in which the length of the pattern is shortened. As a result, the quality and yield of the semiconductor devices are deteriorated. In order to solve the above problems, that is in order that a pattern having a desired shape may be printed onto the semiconductor substrate, an optical proximity correction is compensatorily provided, wherein the pattern printed on the mask is predistorted in the direction opposite to which the lens is curved, and a mask having such a distorted pattern is known as an optical proximity correction mask.
With reference to the accompanying drawings, some conventional optical proximity correction masks will be described.
FIG. 1A illustrates the layout of a typical mask without optical proximity correction, wherein main patterns 2 which serve as a light blocking layer are formed on a transparent mask plate 1. FIG. 1B illustrates the shape of the pattern printed onto a semiconductor substrate by irradiating the mask shown in FIG. 1A. That is, the main patterns 2 of the mask when printed onto the semiconductor substrate 10 have the shape of the patterns 40. In order to easily compare the main pattern 2 of the mask with the patterns 40 printed onto the semiconductor substrate 10, the two patterns are superimposed with the main pattern 2 shown by dashed lines in FIG. 1B. Here, the shape of the main pattern 2, to be obtained on the semiconductor substrate 10 by using the mask of FIG. 1A, is a rectangle having square corners. However, the pattern 40 which is actually printed onto the semiconductor substrate has excessively rounded corners due to the optical proximity effect.
When corners are excessively rounded as in the patterns 40, the length and width of the patterns may be shortened, thereby decreasing the reliability of the semiconductor device.
Accordingly, an optical proximity correction mask may be utilized to solve the above problem. FIG. 2A is a diagram illustrating a conventional optical proximity correction mask, and FIG. 2B illustrates a pattern printed onto a semiconductor substrate by using the mask in FIG. 2A.
As shown in FIG. 2A, the main patterns 2 serving as the light blocking layer are formed on the mask plate 1, and subsidiary patterns 3 are formed joined to the line edge of each corner of the main patterns 2. Here, as shown in FIG. 2A, the subsidiary pattern 3 outwardly distorts from the line edges of the main pattern 2 to compensate for the effect that when printing the pattern 2 onto the semiconductor substrate, the shape of the thusly printed pattern has rounded corners, thus being inwardly distorted compared to the main pattern 2. As shown in FIG. 2A, the conventional optical proximity correction mask is provided by joining the subsidiary patterns 3 to the line edges of the main patterns 2. FIG. 2B illustrates the pattern 50 printed onto the semiconductor substrate 10 by using the conventional optical proximity correction mask of FIG. 2A. To easily compare the pattern 50 to the main pattern 2 of the mask, the two patterns are superimposed with the main pattern 2 shown by dashed lines in FIG. 2B. The corner rounding error of the pattern 50 printed on the semiconductor substrate 10 is improved compared to the pattern 40 of FIG. 1B which is printed by using the plane mask. However, the width and length of the pattern 50 are wider and longer than that of the actual mask, thus the pattern 50 is outwardly formed larger than the main pattern 2 of the mask, causing what is called an over-shoot. Accordingly, in order to overcome the over-shoot, another subsidiary pattern for correction may be added to the main pattern 2 of the mask, or the size and/or number of the subsidiary patterns 3 previously provided may be reduced. That is, a repetition of adding and removing a new subsidiary pattern to and from a proper position must be formed until the pattern 50 printed onto the semiconductor substrate 10 approximates to the main pattern 2 of the mask plate 1 as shown in FIG. 2A. The above problem results because a lens is used in the light exposure apparatus, and thus the optical proximity effect occurs. FIG. 3A illustrates a plane layout of a typical mask having complicated-shaped main patterns, and FIG. 3B illustrates an example of the conventional optical proximity correction mask after applying a plurality of subsidiary patterns to the mask of FIG. 3A.
Since a large number of subsidiary patterns are employed for the conventional optical proximity correction mask, the amount of data required for generating the mask patterns is increased, and thus the data processing speed slows down, and a mask test becomes harder. In addition, when the main patterns are close to each other, the distance between adjacent patterns becomes narrower as the subsidiary patterns are added thereto, and therefore a pattern bridge or a butting of the patterns can arise, whereby the resolution of the mask is deteriorated.